JPS6333998A - Piezoelectric speaker - Google Patents

Abstract

PURPOSE:To improve the acoustic conversion efficiency by coupling an outer periphery of a piezoelectric vibrator to a drive part of an acoustic diaphragm via an elastic material made coupler, forming a small air chamber by the coupler, the piezoelectric vibrator and the acoustic diaphragm and leading the small air chamber to external air by a vent provided to the diaphragm. CONSTITUTION:The outer peripheral edge 4a of the piezoelectric vibrator 4 is adhered and fixed to the upper end face of the cylindrical coupler 8 made of an elastic material such as rubber directly. A sub tone P1 of a high sound frequency is generated in the small air chamber 12 by a force F caused in the outer peripheral edge 4a of the piezoelectric vibrator 4. The tone P1 is radiated to external air through a ring gap 11 of the open hole 10 made to a honey-comb diaphragm 1, which has less split vibration and the main tone P0 and the sub tone P1 are operated at a normal phase relation, then the attenuation of the high frequency tone by the coupler 8 is compensated. Thus, the frequency response with corrected high sound frequency is obtained and nearly flat acoustic characteristic is obtained over the entire frequency band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric speaker in which a piezoelectric vibrating element is coupled to a driving portion of an acoustic diaphragm via a bonded body of elastic material.

[Prior Art] Conventionally, piezoelectric ceramic diaphragms have been made by attaching a thin film body, in which an electrode surface is adhered to a piezoelectric ceramic, to both sides of a metal plate, such as a brass plate, with approximately the same thickness and similar elastic modulus. Bimorph type) or one side (unimorph type). Such a piezoelectric ceramic diaphragm has a large elastic modulus, and its natural vibration frequency fo is inevitably on the high end of the audible range (usually 2KH2 or higher), and it is also brittle and easily damaged mechanically. It is something. This is a significant obstacle to the practical application of piezoelectric ceramic speakers using piezoelectric ceramic diaphragms.

The applicant of the present invention previously proposed a piezoelectric vibrating element as disclosed in Japanese Patent Application No. 59-186979 in order to solve the above-mentioned problems. As shown in FIG. 5, this device is made up of a circular or rectangular piezoelectric plate (pressure! diaphragm) 5 with a weight 7 as a variable impedance element attached near the center of gravity via a viscoelastic layer 6. This is a piezoelectric vibrating element 4.

By restricting the degree of freedom of movement near the center of gravity of the piezoelectric plate 5, this piezoelectric vibrating element 4 generates vibration in a concave lens-like curved deformation mode, and the outer peripheral edge of the piezoelectric vibrating element 4 The active element has a vibration constant such that the excitation force F from 4a corresponds to the vibration frequency in the audible band and has approximately constant velocity. If the piezoelectric vibration element 4 having such a configuration is applied as an excitation source to an acoustic transducer such as a piezoelectric speaker or a piezoelectric microphone, the operating frequency band can be easily expanded and high acoustic conversion efficiency can be obtained. .

[Problems to be Solved by the Invention] When configuring an acoustic transducer using the piezoelectric vibrating element 4 as described above, the outer peripheral edge 4a of the piezoelectric vibrating element 4 is directly connected to the driving part of the acoustic diaphragm. Then, an outer periphery reflection phenomenon at the outer periphery 4a of the piezoelectric vibrating element 4, which is observed when transmitting and receiving vibration energy, appears, and standing wave vibration occurs at a specific frequency, which not only increases the vibration transmission loss. There is a problem in that the piezoelectric ceramic layer is prone to breakage due to abnormal vibrations and failures such as reduced sensitivity. In particular, when the piezoelectric vibrating element 4 is applied to a honeycomb diaphragm with a large mechanical impedance in the driving part, there is a risk that the piezoelectric vibrating element 4 will be damaged due to overload operation, and the acoustic characteristics in the high frequency range will deteriorate. There was a problem in that a sufficient dynamic range could not be obtained in its operation.

This invention was made to solve these problems, and because of its structure as a piezoelectric acoustic transducer, it prevents the generation of harmful standing wave vibrations, reduces vibration transmission loss, and improves acoustic conversion efficiency. The purpose of the present invention is to obtain a piezoelectric speaker that can improve the performance of the piezoelectric plate, prevent damage and deterioration of the piezoelectric plate, reduce deterioration of high-frequency acoustic characteristics, and expand the dynamic range.

[Means for Solving the Problems] A piezoelectric speaker according to the present invention includes a piezoelectric vibrating element and an acoustic diaphragm drive unit, each of which includes a weight attached to the center of gravity of the piezoelectric vibrating element via a viscoelastic layer. When coupling the piezoelectric vibrating element, the outer peripheral edge of the piezoelectric vibrating element is coupled to the driving part of the acoustic diaphragm through a coupling body made of an elastic material such as rubber, and the piezoelectric vibrating element and the acoustic diaphragm are connected to this coupled body. A small air chamber is formed surrounded by a diaphragm, and the small air chamber is connected to the outside air through an opening provided in the acoustic diaphragm.

[Function] In the piezoelectric speaker of the present invention, the outer peripheral edge of the piezoelectric vibrating element is coupled to the driving portion of the acoustic diaphragm via a coupling body made of an elastic material such as rubber, and the coupling body and the piezoelectric A small air chamber is formed surrounded by the vibration element and the acoustic diaphragm, and the small air chamber is configured to communicate with the outside air through an opening provided in the acoustic diaphragm. It prevents the generation of harmful standing wave vibrations, reduces vibration transmission loss, and improves acoustic conversion efficiency.It also prevents damage and deterioration of the piezoelectric plate, and reduces the acoustic characteristics in the high frequency range. can be reduced and the dynamic range expanded.

[Example] Now, the acoustic honeycomb diaphragm known in -m is as follows.
A large number of hexagonal honeycomb-shaped cells made of kraft paper or the like are connected to form a core (core member), and a skin is attached to both sides of the core, and this type of honeycomb diaphragm has extremely high bending rigidity. Moreover, since it is lightweight, it has excellent characteristics as a flat plate type diaphragm, and has recently been widely used in various fields. By the way, if the outer peripheral edge of the piezoelectric vibrating element is directly attached to this honeycomb diaphragm and excitation is performed,
The difference in mechanical impedance at the connection point between the piezoelectric vibrating element and the honeycomb diaphragm can result in a so-called mismatching condition, which can lead to many of the problems described above.

However, the piezoelectric speaker according to the present invention can eliminate the above-mentioned problems.

FIG. 1 is a cross-sectional perspective view showing a piezoelectric speaker according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a honeycomb diaphragm, which is constructed by covering both surfaces of a core 2 with skins 3a and 3b. Reference numeral 4 denotes a piezoelectric vibrating element formed by attaching a weight 7 to the vicinity of the center of gravity of a piezoelectric plate 5 (circular in this case) via a viscoelastic layer 6.

Reference numeral 8 denotes a short cylindrical joint made of an elastic material such as rubber, and the outer peripheral edge 4a of the piezoelectric vibrating element 4 is directly attached and fixed to the upper end surface of this joint 8.

Furthermore, the bottom surface 9 of the combined body 8 is a flat surface, and is tightly bonded to the driving surface of the honeycomb diaphragm 1. An opening 10 is formed in the substantially central portion of the honeycomb diaphragm 1 so as to look through the weight 7, and a narrow annular gap 11 is formed around the weight 7 in a non-contact state. In this way, the coupling body 8 is placed on the top surface of the piezoelectric vibrating element 4.
A small air chamber 12 of small capacity is formed surrounded by the honeycomb diaphragm 1 and the honeycomb diaphragm 1, and this small air chamber 12 communicates with the outside air through the annular gap 11 of the opening 10. 13a and 13b are signal voltages e to the piezoelectric vibrating element 4; This is a flexible lead wire for applying . Further, the outer peripheral edge of the honeycomb diaphragm 1 is connected to a frame 15 via a corrugated edge 14, so that it is always held in a fixed position.

In such a configuration, this winter leader line 13a.

If signal voltage eQ is applied to question 13b, piezoelectric vibrating element 4
The vibrational force F generated on the outer peripheral edge 4a of the honeycomb diaphragm 1 is transmitted to the honeycomb diaphragm 1 via the coupling body 8, and as a result, the honeycomb diaphragm 1 is excited and emits the tonic sound Po to the outside on its upper surface side. It will radiate.

In this case, the combined body 8 acts as a buffer between the hard honeycomb diaphragm 1 and the easily bendable piezoelectric vibrating element 4, and facilitates the deformation vibration of the piezoelectric vibrating element 4, thereby reducing its viscoelasticity. This effect absorbs and calms the standing wave vibration, suppresses excessive amplitude, and prevents damage and deterioration of the piezoelectric vibrating element 4. Furthermore, physically speaking, the combined body 8 acts as a kind of impedance converter, and the mismatch between the piezoelectric vibration element 4 and the honeycomb vibration plate 1 (
mismatching) and improve vibration transmission efficiency.
This means that it helps improve the acoustic conversion sensitivity of the speaker. Although the material of the coupling body 8 differs depending on the application conditions, it is desirable to use a material that satisfies the two conflicting conditions of vibration energy absorption and transmission in the normal temperature operating range, and is usually made of JIS rubber. Approximately 30 on the hardness scale
Practically satisfactory results have been obtained by using synthetic rubbers such as nitrile-based, polyurethane-based, and neorene-based rubbers having an angle of about 40° to 40°.

Note that here, since the bonding body 8 is made of an elastic material such as rubber, the tonic tone P. The absorption loss of the high-frequency sound increases somewhat and the transmission to the honeycomb diaphragm 1 decreases, so the frequency response of the radiated sound pressure gradually attenuates slightly in the high-frequency range as shown in the frequency response shown in Figure 2. The acoustic characteristics are as follows.

By the way, on the other hand, due to the excitation force F generated at the outer peripheral edge 4a of the piezoelectric vibrating element 4, a high-pitched subtone Pl is generated in the small air chamber 12. This subtone P1 is radiated to the outside air through the annular gap 11 of the opening 1o formed in the honeycomb diaphragm 1.

Here, the honeycomb diaphragm 1 has few divided vibrations, and the tonic P
. and the subtone P1 operate in a normal phase relationship, so the attenuation of the high frequency by the coupling body 8 as described above is compensated, and as a result, the high frequency response as shown in the shaded area of the surrounding wave number response I shown in FIG. A corrected frequency response can be obtained, and a substantially flat acoustic characteristic can be obtained over the entire desired frequency band. In this case, since the small air chamber 12 and the annular gap 11 operate as a so-called Helmholtz resonator, the annular gap 11 exhibits a constriction effect, increasing the molecular velocity of the air flowing in and out. can improve radiation efficiency. Furthermore, the radiation impedance of the aperture 1o determines the upper limit f of the frequency response correction band shown in FIG. When the annular gap 11 is usually about 11, the upper limit f of the correction band is about 8 to 10 KHz. Also,
As in another embodiment of the invention shown in FIG.
If the sitting height of the honeycomb diaphragm is high and there is a gap 11a between the weight 7 and the honeycomb diaphragm 1, a small diameter opening 10a is opened,
Due to the narrowing effect, the upper limit f of the correction band can be brought to an appropriate frequency.

In the above embodiment, the honeycomb diaphragm 1 is used as the acoustic diaphragm. However, as in another embodiment of the invention shown in FIG. 4, a cone diaphragm 16 is used as the acoustic diaphragm. It's okay.

That is, a lightweight perforated plate 17 is placed on the top of the cone diaphragm 16.
It is also possible to form a small air chamber 12 by providing a subtone P1. However, the cone diaphragm 16 usually has many divided vibrations, and the tonic tone P has a phase rotation.

There may be irregularities in the overall characteristics of the subtone P1.

Further, in the embodiment described above, each of the openings 10 and 10a may be covered with a dust cap made of non-woven fabric or the like, if necessary, and used as an acoustic resistor to adjust the treble correction amount.

[Effects of the Invention] As explained above, the present invention provides a piezoelectric speaker in which the outer peripheral edge of the piezoelectric vibrating element is coupled to the driving portion of the acoustic diaphragm via a coupling body made of an elastic material such as rubber, and A small air chamber is formed surrounded by this combined body, a piezoelectric vibrating element, and an acoustic diaphragm, and the small air chamber is configured to communicate with the outside air through an opening provided in the acoustic diaphragm, so that piezoelectric acoustic conversion is possible. Due to the structure of the device, it is possible to prevent the generation of harmful standing wave vibrations, reduce vibration transmission loss and improve acoustic conversion efficiency, and prevent damage and deterioration of the piezoelectric plate.
This has excellent effects such as reducing the deterioration of acoustic characteristics in the high frequency range and expanding the dynamic range.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional perspective view showing a piezoelectric speaker according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the frequency response of the piezoelectric speaker shown in FIG. 1, and FIG. Sectional view showing the main parts of the piezoelectric speaker according to the embodiment, No. 4
The figure is a cross-sectional view showing a piezoelectric speaker according to another embodiment of the present invention, and FIG. 5 is a schematic diagram showing the configuration of a piezoelectric vibrating element to which the present invention is directed. In the figure, 1... honeycomb diaphragm, 2... core,
3a, 3b... Epidermis, 4... Piezoelectric vibration element, 4a.
...Outer peripheral edge of piezoelectric vibrating element 4, 5...piezoelectric plate, 6.
... Viscoelastic layer, 7... Weight, 8... Combined body, 9...
・Bottom surface of combined body 8, 10.10a...opening, 11...
・Annular gap, 11a... Gap, 12... Small air chamber, 1
3a, 13b...Leader line, 14...Edge, 15
...Frame, 16...Cone diaphragm, 17...
It is a perforated plate. In each figure, the same reference numerals indicate the same or equivalent parts. Patent applicant: Sawafuji Dynameka Co., Ltd.
I, Kiyu 3a, 3b: Lli
13a, 13b: Drawer demon 4: Mr. Liu vs. Luo J14: Engineering, 2
Ji4o: Voice U Zanku S4's Sotohobu 15: Frame 5
: Kawara 1n Fire 6: Kushosa layer 7: Number of layers 8: Tokai person 9: 8 ward H book 8 threads, tl 10: Closed hole No. 2rjA Fig. 3 100: Bunkou 11o: Mongyo

Claims (1)

[Claims] The outer periphery of the piezoelectric vibrating element, which has a weight attached to the vicinity of the center of gravity of the piezoelectric diaphragm via a viscoelastic layer, is connected to the driving part of the acoustic diaphragm through a combination of elastic materials. A piezoelectric speaker characterized in that a small air chamber is formed surrounded by a combined body, the piezoelectric vibrating element, and an acoustic diaphragm, and an opening is provided in the acoustic diaphragm through which the small air chamber communicates with the outside air. .